1. Field of the Invention
The present invention relates to a stepping motor control and more particularly to a printing control for an information processing apparatus such as a facsimile or copying machine using a stepping motor.
2. Description of Related Art
Generally, in a printing apparatus incorporated in a facsimile, copying machine or the like, a stepping motor is used for mechanisms for conveying an original document and a printing paper, and the CPU performs conveyance control thereon according to a control program.
Especially, in a printing apparatus incorporated in a facsimile or copying machine arranged to execute processes other than a printing process, there are a mode for supplying an original document, a mode for reading the original document to be transmitted or copied, a mode for discharging the original document, a mode for supplying a printing paper, a mode for cueing the printing paper, a mode for printing onto the printing paper, a mode for discharging the printing paper. Further, there are other modes in which these modes are executed in combined forms, whereby a number of complex conveyance processes based on the use of the stepping motor are executed while those relevant modes are being changed over. The stepping motor is subjected to a higher mechanical load in the copying (reading and printing) mode than in the printing mode, because it drives two conveyance mechanisms for reading and printing in the copying mode.
In this printing apparatus, when the printing apparatus stops its operation for some reason at the time of switching from one mode to the next mode, it is likely to occur that the excitation current to the stepping motor continues to be supplied unnecessarily to the stepping motor. If this continued supply of the excitation current lasts long, the stepping motor will heat up causing damages therein or to the peripheral devices.
It is proposed to stop the supply of the excitation current to the stepping motor at the end of each mode, so that the above damages may not be caused. For instance, in the printing apparatus mounted in the facsimile or the like which performs the printing process for printing information on a printing paper by a printing unit, reading process for reading information on an original document by a reading unit and copying process for reading and printing simultaneously, the excitation current to the stepping motor is stopped at every completion of modes of the above processes.
Although stopping the excitation current at every switching from one mode to another do not cause any asynchronization between the excitation current and the rotation of the stepping motor in the printing process or in the reading process, the stopping is likely to cause the asynchronization in the copying process resulting in nonuniform paper or document feeding speed.
While the stepping motor drives only one of a printing paper conveyance mechanism and an original document conveyance mechanism in each mode for the printing process or the reading process, while it drives both of the conveyance mechanisms in the copying mode in which reading and printing are attained simultaneously.
As a result, when the stepping motor starts to rotate upon reenergization by the excitation current after stopping of the previous energization at the time of switching to the copying mode, the stepping motor is likely to rotate asynchronously with the excitation current at the starting period in the copying mode. This results from the facts that the stator and the rotor are not held in position by the electromagnetic attraction therebetween due to discontinuation of the excitation current supply, and the stepping motor receives a high mechanical load from both of the conveyance mechanisms at the start of the copying mode.
The similar problem also occurs in various systems using a stepping motor for driving selectively a plurality of mechanisms.